The present invention generally relates to wireless communication receivers, and particularly relates to automatic gain control of such receivers.
Most communication receivers use some form of automatic gain control (AGC) to maintain received signals within a desired range. For example, a typical wireless communication receiver obtains digitized samples of a received signal of interest based on digitizing a baseband analog signal derived from an incoming analog received signal of interest, e.g., an antenna receiving an over-the-air communication signal.
Those skilled in the art will appreciate that satisfactory digitization depends on maintaining the analog input signal within a defined signal (voltage) range that is appropriate for the analog-to-digital converter (ADC) being used to digitize the signal. On the one hand, the analog input signal must be kept below the upper voltage limit of the ADC's input range to avoid saturation, and on the other hand, the analog input signal must be kept at a high enough signal level for acceptable quantization accuracy. That is, the input signal's range generally should span all or nearly all of the defined input voltage range of the ADC to realize the full quantization accuracy of the ADC. For example, a 10-bit ADC configured for a 0-to-5 Volt input signal range operates with an effective resolution of 9 bits or less if the actual input signal range is only 2.5 Volts.
In this context, then, an AGC circuit is configured to track the incoming received signal strength, for example, and to adjust one or more receiver gain elements as needed to maintain a desired input signal range to the ADC. Of course, AGC has applicability beyond controlling the input signal range for receive chain ADCs, and may be used to prevent the saturation of analog amplifiers, filters, etc., within the receive chain, such as by varying the gain of one or more amplifier or preamplifier stages.
However applied, convention AGC functions may be upset by significant disruptions in the signal being used as the reference for AGC. For example, the temporary loss of the received signal causes the convention AGC function to ramp receiver gain upward in an attempt to boost the low or non-existent received signal strength. While that behavior represents proper AGC functionality, it can cause temporary saturation problems when the received signal returns. Similar kinds of under- or over-boosting problems arise with other types of signal disruptions, such as signal jamming, etc., wherein the conventional AGC function may suffer undesirable control lags with respect to the transitions between abnormal (disrupted) and non-disrupted (normal) signal conditions.